1. Field of the Invention
The present invention generally relates to a system for the electronic display of prices on shelves, with a computer, a control transmitter connected to the computer and electronic display units fastened to the edges of the shelves, whereby at least the shelves equipped with display units are provided with electrically conducting transmitter elements which are fed an alternating current by the control transmitter and emit electromagnetic energy, whereby the control transmitter, by means of the transmitter elements, transmits to the display units data packets which contain the data to be displayed and are separated from one another in time by pauses, and whereby in each of the respective display units there is a component to receive the energy emitted by the transmitter elements. This component feeds a charging current to a rechargeable power supply. The power supply provides at least a portion of the operating current of the display unit.
2. Background Information
In the field of modern retailing, the increasing use of bar codes to identify the type and the price of products has resulted in the diminished use of individual price tags or stickers on each item of merchandise. To indicate the price of an item, a tag or label is usually affixed to the edge of the shelf on which the item is located.
However, there is generally no guarantee that the price on the label is the same as the price stored in the store computer which is used to charge the customer at the checkout. This can lead to customer complaints and possible legal action against the retailer. Moreover, when prices change, the replacement of the tags or labels on the shelf edges can generally be relatively labor-intensive, since each tag or label must essentially be prepared and replaced manually.
Accordingly, electronic price display signs have been developed which can be affixed instead of the conventional signs to the edge of the shelf, and which optically indicate the price of the merchandise and perhaps additional information. Since the electronic display units are connected to the store computer, it can generally be guaranteed that the price displayed on the sign is the same as the price which will be charged at the checkout. The central computer can also easily update the information on the respective display unit. This updating is usually done by means of a transmission which includes the specific address code for the respective display unit or the respective group of display units, as well as the price information for the merchandise in question. In this manner, it is possible to modify the indicated prices, such as for a special sale with reduced prices, with little expense or effort.
U.S. Pat. No. 4,500,800 discloses such electronic display systems which are physically connected by wires to a power source and to the store computer. One disadvantage of these systems is that the hard-wired connection is cumbersome if the tags must be moved frequently. Furthermore, the contacts between the display tags and the connecting wires are subject to wear and tear, which results in errors in the transmission of data and/or energy to the signs.
A generic system of this type is disclosed in Federal Republic of Germany Patent No. 37 31 852 A1, which corresponds to U.S. Pat. No. 4,821,291. To eliminate the hard wiring of the display units, the display units are powered with electrical energy by means of internal batteries. The information to be displayed is transmitted by electromagnetic waves which are emitted by the control transmitter connected to the central computer by means of wires laid above the shelves. The data are transferred in packets--corresponding to the display units to be updated--and between the data packets there are pauses during which no waves are emitted. As an alternative to batteries, the power supply for the display units can be in the form of storage batteries or capacitors of sufficiently high capacity, which are recharged during the transmission of the data packets by means of the electromagnetic energy received. In the generic system, the display units are also recharged with electromagnetic energy by a separate transmitter outside operating hours.
The primary disadvantage of such a system is the inefficiency of the transmission of energy to the display units. Since the wires used as the transmission elements are laid on the top of the shelves and are also shielded by the shelves, it is generally necessary to use a correspondingly high transmitter power to recharge the power source and for the error-free transmission of data, to achieve sufficiently high field strengths in the relatively distant display units. This essentially means that, on one hand, complex technical measures and high energy levels are required, and on the other hand, that other electronic devices (such as scales or cash registers) located in the vicinity could be affected by induced voltages. In addition, recharging is generally only possible during the transmission of the data packets, which further increases the field strengths which must be emitted. Store personnel and customers can also be exposed to the effects of relatively intensive electromagnetic fields. If the recharging process is performed before and after business hours, on the other hand, large and expensive storage batteries and capacitors with a high charge capacity are generally necessary to guarantee the operation of the display units throughout business hours.